(a) Field of the Invention
The present invention relates to a mobile station executing an alarm processing of a degraded communication quality. The present invention also relates to a method for representing an electric field level on a display unit of the mobile station.
(b) Description of the Related Art
A user of a mobile station generally knows the intensity (or level) of the electric field of a radio signal received in the mobile station by observing an image of antenna bars represented on the display unit of the mobile station. If the electric field level represented on the display unit is lower, the user accepts the state of disconnection of the link to the mobile station as an unavoidable fact. If the electric field level is higher, to the contrary, and yet the link to the mobile station is in the state of disconnection, the user will consider this fact as an abnormal state.
Similarly, the user accepts a disconnection or an alarm of disconnection of the link as well as degradation in the communication quality thereof during performing the communication, if the electric field level represented on the display unit is lower. However, the user cannot accept such a disconnection or an alarm of disconnection during performing the communication if the electric field level represented on the display unit is higher, feeling uncomfortable or receiving a strong stress upon generation of the disconnection or alarm of disconnection.
As used in some mobile stations, there is a technique for measuring the signal level of the common channel transmitted from the base station by measuring an RSSI (received signal strength indicator) or RSCP (received signal code power), to represent the intensity of the electric field on the display unit, while using the measured RSSI or RSCP as a reference. This technique is described in Patent Publication JP-A-2002-374575, for example.
In the mobile network system notifying the user of the state of radio signal (or electromagnetic wave) by using the technique as described above, the user can recognize the state of radio signal and may accept the possibility of disconnection by observing the indication on the display unit.
There is another technique used in the mobile network system for detecting a degraded communication quality by using a bit error rate in the received signal during the communication, notifying the user of the degraded communication quality by using a sound alarm, for example. This technique is described in Patent Publications JP-A-9(1997)-233018 and -6(1994)-61938, for example.
FIG. 10 shows a flowchart of the another technique for detecting a degraded communication quality. It is first judged whether or not the mobile station is in the state of communication (step S51). If the judgement in step S51 is, negative, the process advances to step S55 to set the flag of the degraded communication quality at an OFF (set the flag Q_ALM=OFF), for executing an alarm stop processing. It is to be noted that the alarm stop processing is such that an alarm for a degraded communication quality is not generated or an existing alarm is stopped. The alarm may be a sound alarm, or a light alarm emitted from an LED (light emitting diode), notifying the use of the degraded communication quality during the communication.
On the other hand, if the judgement in step S51 is affirmative, CRC (cyclic redundancy check) tests are performed on the received data to count the number of errors (NGs) per unit time period in the received data. The length of the unit time period is arbitrarily determined. This CRC-NG test is completed for every unit time period, and the number of NGs of the unit periods are accumulated and stored as a variable CRC (step S52).
The variable CRC is then compared against a threshold CRCth (step S53). If CRC<CRCth is judged in step S53, then the process advances to step S55 wherein the alarm is not generated or stopped, whereby the flag Q_ALM=OFF. If CRC≧CRCth is judged in step S53, then the alarm for a degraded communication quality is generated, or continued if it has been generated in the earlier cycle, whereby the flag Q_ALM=ON.
FIG. 11 shows a flowchart of the technique for representing the electric field level on the display unit. First, the mobile station detects the electric field level Level (step S61). The detection is performed periodically, or may be performed continuously. The detected electric field level, which may be detected by measuring an RSSI or RSCP, is stored as a variable Level.
It is judged in step S62 whether or not the variable Level is lower than a first threshold Lth1. If the judgement in step S62 is affirmative, the process advances to step S63, wherein the variable, or detected electric field level, Level is represented as level-1 on the display unit, the level-1 meaning the lowest electric field level. If the electric field level is to be visually represented on the display unit, the level-1 may be represented by a single antenna, whereas level-2 and level-3 may be represented by two antennas and three antennas, respectively, for example, thereby showing the intensity level of the electric field.
If the judgement in step S62 is negative, the process advances to step S64, wherein it is further judged whether or not the variable Level is lower than a second threshold Lth2 which is higher than the first threshold Lth1. If the judgement in step 64 is affirmative, then the process advances to step S65, wherein the electric field level is represented as level-2, i.e., by two antennas. If the judgement in step S64 is negative, the process advances to step S66 wherein the electric field level is represented as level-3, i.e., by three antennas.
FIG. 12 shows the relationship between the intensity of the electric field and the number of NGs counted in the CRC tests in the conventional mobile station. FIG. 12 also shows the level number represented on the display unit for the intensity of the electric field, at the top of the figure.
In FIG. 12, it is shown that the number of NGs is compared against a threshold CRCth to generate an alarm in the time interval between T1 and T2 and in the time interval between T3 and T4.
The alarm generated in the time interval between T1 and T2 may be accepted by the user, because the electric field level represented on the display unit is level-1. On the other hand, the alarm generated in the time interval between T3 and T4 cannot be necessarily accepted, because the electric field level represented on the display unit is level-3. This alarm provides a sense of discomfort to the user due to the fact that the degraded communication quality occurs under a strong electric field, or a favorable electric field level.
In general, the level of electric field is detected for the common channel of the area where the mobile station is located, whereas the degraded communication quality is detected based on the CRC tests for the specific channel through which the mobile station communicates with the base station. More specifically, the electric field level or state of the electric field may have a discrepancy between the common channel and the specific channel in some cases. This is the reason that the user feels the sense of discomfort in the alarm informing the degraded communication quality.